1. Field of the Invention
Laminate structures having improved dynamic properties, specifically increased resonant frequencies and higher damping, and more particularly laminate structures comprising weldable metals and a method for making the laminates.
2. Prior Art
The need for laminate structures made in accordance with the present invention is exemplified by discussing the performance limitations of structures made in accordance with the prior art in a representative application. Accordingly, while the limitations of prior art structures used in computer disk drives is presented as an exemplary application for the laminate structures of the present invention, the limitations inherent in prior art monolithic (i.e., non-laminate) structures, particularly in regard to their vibrational properties, similarly limits the performance of prior art structures in other applications. Although the present invention is discussed in the context of a particular application, the particular application is exemplary and should not be construed as limiting the scope of the invention.
At the present time, most computer systems store data on a disk drive. A disk drive includes inter alia a rotatable disk, and an actuator that moves a transducer over the surface of the disk. The rate at which data can be transferred to the disk drive depends, in part, on the dyanamic performance of the actuator. Stiffer actuating systems with higher resonant frequencies allow the transducer to be moved at higher speeds, facilitating higher rates of data transfer. In addition, increased damping characteristics of the actuator limit excursions of the load beam and shorten transducer settling time-both of which increase drive performance. These features will also help to accommodate the increasing demand for higher areal densities prevalent in the disk drive industry. Moverover, disk drives sometimes operate in hazardous environments that may include being dropped from several inches. Such shock loads, when experienced during disk operation, may drive a resonant response in the loadbeam. Notwithstanding these excitations, the load beam, and the transducer attached thereto, must maintain the transducing relationship between the transducer and the surface of the disk at all times. Higher stiffness suspension systems with increased damping capacity help to limit the elevational excursions of the load beam that may cause damage to the surface of the disk, the transducer and/or the load beam, or the lateral excursions of the load beam that may cause data track mis-registration and read-write errors. It is, therefore, desirable to provide a material for fabricating a load beam, mounting arm and/or flexure having a high stiffness and damping capacity.
Material damping occurs when repetitive deformation (vibration) of a material is dissipated through internal energy losses, usually in the form of heat. In general, the phenomenon of damping, also known as internal friction, can be characterized by a lag between the application of a stress and the resultant strain. The mechanisms that give rise to damping in metals include the interaction of specific point defects with other point defects or dislocations, precipitation phenomena, and ordering effects. Thus, prior art efforts to produce structures having desired damping characteristics include developing new alloy compositions and laminate structures that attempt to enhanse these mechanisms, thereby improving damping properties.
Transient liquid phase diffusion bonding has been shown to be a useful method for producing high quality diffusion bonds in high temperature metal laminate structures. Such bonding is described in detail in the U.S. Pat. No. 3,678,570 to D. F. Paulonis et al, and is incorporated herein by reference thereto. Barlow et al., in U.S. Pat. No. 4,208,222, disclose a method for carrying out transient liquid phase diffusion bonding by depositing a metallic coating on at least one of the superalloy surfaces to be bonded and boriding a portion of the metallic coating to form a working coating having an overall composition resembling that of an interlayer alloy and an overall melting temperature less than that of the superalloys. When the superalloy surfaces are placed in contact and heated to above the melting temperature, the partially borided metallic coating functions as an interlayer alloy to effect bonding.
Ryan, in U.S. Pat. No. 4,700,881, discloses an improvement of transient liquid phase bonding through the use of multiple boronized interlayer foils. By providing the interlayer in the form of multiple foils a reservoir of liquid material is formed during the bonding process which eliminates the porosity encountered with traditional transient liquid phase bonding such as described in U.S. Pat. No. 3,678,570, referenced above. The use of multiple foils is especially appropriate when bonding fine-grained materials at constant temperature. By using two foils, each of which has boronized surfaces, upon heating to elevated temperatures the assembled foils melt, both at their outer portions which are adjacent the articles being joined, and at the interface between the two foils. By providing a boron rich zone and consequently a liquid zone in the center of the foil assembly, the previously encountered tendency to form porosity is essentially eliminated. The process has particular utility in the bonding of fine-grained superalloy articles in which porosity has previously been a problem.
Gaynes et al., in U.S. Pat. Nos. 5,713,508 and 5,542,602 disclose a method for forming a metallurgical bond between two metal surfaces including the steps of placing a metal coating on at least one of the surfaces, applying a compressional force to the juxtaposed metal surfaces, and alloying the metal coating with both of the two metal surfaces at a temperature at or below 237xc2x0 C. The coating materials employed include indium, tin and lead. A device is provided including a metallurgical bond between two bodies of noble metal including a region extending into the two bodies of noble metal comprising an alloy of noble metal and a metal selected from the group consisting of indium, tin and lead.
Diffusion causes a transient liquid phase to be interposed in the interface. Accordingly a flow of the transient liquid phase can correct the irregularities, asperities, or other undesired structural aspects in the abutted surfaces. Fitzgerald et al. U.S. Pat. No. 5,836,075, teach machining of the mating surfaces prior to application of the bonding material to remove oxide from the mating surfaces and ensure dimensional tolerances. Bonding material is applied to the mating surfaces by sputter deposition. A mask(s) may also be applied to the mating surfaces prior to application of the bond material so as to selectively apply bond material at only predetermined locations on the mating surface, thus eliminating excessive use of bond material for bonding the component sub-structures.
Bampton et al., in U.S. Pat. No. 5,289,967 disclose a method for fabricating metal matrix composites. Optical or reinforcing fibers, which may be in the form of monofilaments, mats, or tow, are consolidated into a metal matrix alloy. Grooves may be provided in the metal matrix material for holding and positioning the fibers. A transient liquid diffusion bonding agent in the form of a powder is blended with powdered filler material, such as powdered matrix material, to provide a vehicle for consolidating the fibers into the metal matrix. The fibers and the blended powder are placed between layers of the metal matrix material and the whole structure is heated under minimal pressure to liquefy the bonding agent. The liquid bonding agent wets each fiber and interdiffuses with the matrix material, resulting in rapid isothermal solidification of the alloy and consolidation of the fibers in the matrix.
As discussed above, for certain applications such as computer disc drive components, it is desirable to employ structural components which exhibit higher frequency fundamental vibrational modes. In addition, components comprised of a material that damps vibrational energy are preferable for fabricating disk drive suspension arms. Accordingly, there is a current demand for a laminate structure having a high damping core interposed between stiff outer layers that is suitable as a structural element in such applications.
It is a primary object of the invention to provide.metal laminate structures having vibrational and damping properties suitable for use in applications where increasing the vibrational resonant frequencies of the structure is desirable.
It is another object of the invention to provide metal laminate structures that undergo minimal outgassing or degradation after the production thereof.
It is yet a further object of the invention to provide a method for making a laminate structure meeting the above objectives wherein the structure comprises a high damping core interposed between two stiff, possibly weldable sheets of metal.
It is another object of the invention to provide a laminate structure comprising a core consisting essentially of a layer of Cuxe2x80x94Mg alloy disposed between two layers of stainless steel and having unitary construction.
To make the laminate structures, copper plated surfaces of metals such as stainless steel are placed in contact with an interposed layer of magnesium and the Cu and Mg allowed to interdiffuse at elevated temperatures. The metals are chosen such that diffusion creates an alloy with a melting point lower than either of the constituents. The processing temperature is set so that the Cuxe2x80x94Mg alloy melts but leaves the base metals in solid form, causing a thin layer of liquid to form.and wet both sides of the interface. External pressure is applied to the opposing base metals and continued diffusion elevates the melting temperature of the liquid phase and causes it to solidify isothermally, creating a bond between the base metals. The pressure induces flow of the liquid phase in order to disrupt an oxide layer on the surface of the interlayer or base metals. Highly polished surfaces on the base metals comprising the laminate structure are not required because the applied pressure causes the metal (in thin sheet form) to deform and create the intimate metal-metal contact necessary for diffusion.
The features of the invention believed to be novel are set forth with particularity in the appended claims. However the invention itself, both as to organization and method of operation, together with further objects and advantages thereof may be best be understood by reference to the following description taken in conjunction with the accompanying drawings in which: